Ok I'm having trouble trying figure out how to determine where the transmission starts. Here are a bunch of captured transmissions, using long high = 1 and short high = 0. The blue columns add up to the temperature (x10) and the red columns add up to humidity (so first row, temp = 14.6 degrees, humidity = 51%). I'm sure I've got that right because I've checked with different figures over a day now and it's always correct.
The second block was a) when I brought the transmitter inside and b) when I took the battery out/in to see what would change.
111111111111 1100 1110 0101 [color=blue]0000 1001 0010[/color] [color=red]0011 0011[/color] 1010 0001-
1111 1000 1110 0101 [color=blue]0000 1001 0010[/color] [color=red]0011 0011[/color] 1010 0001---
1111111111 0100 1110 0101 [color=blue]0000 1001 0010[/color] [color=red]0011 0011[/color] 1010 0001----
11111111111 1100 1110 0101 [color=blue]0000 1001 0010[/color] [color=red]0011 0011[/color] 1010 0001------
1111 1010 1110 0101 [color=blue]0000 1001 0010[/color] [color=red]0011 0011[/color] 1010 0001---
1111111 0100 1110 0101 [color=blue]0000 1001 0010[/color] [color=red]0011 0011[/color] 1010 0001---
11 1000 1110 0101 [color=blue]0000 1001 0010[/color] [color=red]0011 0100[/color] 0011 0110-----
111 0100 1110 0101 [color=blue]0000 1001 0010[/color] [color=red]0011 0100[/color] 0011 0110----
111111 0100 1110 0101 [color=blue]0000 1001 0001[/color] [color=red]0011 0100[/color] 0001 1011---
111 1100 1110 0101 [color=blue]0000 1001 0001[/color] [color=red]0011 0100[/color] 0001 1011------
11111 1010 1110 0101 [color=blue]0000 1001 0001[/color] [color=red]0011 0100[/color] 0001 1011--
1111111111 0100 1110 0101 [color=blue]0000 1001 0001[/color] [color=red]0011 0100[/color] 0001 1011--
1111 1100 1110 0101 [color=blue]0000 1001 0001[/color] [color=red]0011 0100[/color] 0001 1011--
11 0100 1110 0101 [color=blue]0000 1001 0001[/color] [color=red]0011 0100[/color] 0001 1011------
111 1010 1110 0101 [color=blue]0000 1001 0001[/color] [color=red]0011 0100[/color] 0001 1011----
111111111111 0100 0111 0110 [color=blue]0000 1001 0010[/color] [color=red]0011 0100[/color] 0110 1100----
1111111 0100 0111 0110 [color=blue]0000 1001 0010[/color] [color=red]0011 0100[/color] 0110 1100----
11111 0100 0111 0110 [color=blue]0000 1001 0010[/color] [color=red]0011 0100[/color] 0110 1100---
11111111 0100 0111 0110 [color=blue]0000 1001 0010[/color] [color=red]0011 0100[/color] 0110 1100-
111111 0100 0111 0110 [color=blue]0000 1001 0010[/color] [color=red]0011 0101[/color] 0101 1101---------
1111111 0100 0111 0110 [color=blue]0000 1001 0010[/color] [color=red]0011 0101[/color] 0101 1101----
111111 0100 0111 0110 [color=blue]0000 1001 0010[/color] [color=red]0011 0101[/color] 0101 1101-
1111111 0100 0111 0110 [color=blue]0000 1001 0010[/color] [color=red]0011 0101[/color] 0101 1101----
11111111 0100 0111 0110 [color=blue]0000 1001 0100[/color] [color=red]0011 0101[/color] 0000 0111-----
111111 0100 0111 0110 [color=blue]0000 1001 0100[/color] [color=red]0011 0101[/color] 0000 0111------
1111111111 0100 0111 0110 [color=blue]0000 1001 0100[/color] [color=red]0011 0101[/color] 0000 0111-----
1111111 0100 0111 0110 [color=blue]0000 1001 0100[/color] [color=red]0011 0101[/color] 0000 0111-----
1111 0100 0111 0110 [color=blue]0000 1001 0101[/color] [color=red]0011 0110[/color] 1010 0000-------
1111111 0100 0111 0110 [color=blue]0000 1001 0101[/color] [color=red]0011 0110[/color] 1010 0000-----
1111111111 0100 0111 0110 [color=blue]0000 1001 1000[/color] [color=red]0011 0111[/color] 1101 0001------
1111 0100 0111 0110 [color=blue]0000 1010 1000[/color] [color=red]0011 0111[/color] 0110 0011------
111 0100 0111 0110 [color=blue]0000 1010 1001[/color] [color=red]0011 0111[/color] 1001 0111----
111 1100 0111 0110 [color=blue]0000 1010 1010[/color] [color=red]0011 0111[/color] 1011 1010-
11 0100 0111 0110 [color=blue]0000 1010 1010[/color] [color=red]0011 0111[/color] 1011 1010--
1111111 1111 0100 0111 0110 [color=blue]0000 1010 1010[/color] [color=red]0011 0111[/color] 1011 1010---
So I can't make out what the first 4 bits are, they change a fair bit especially when the transmitter was outside (maybe took longer for the AGC to do something because of a weaker signal so those get mixed up?). The next 8 seem to be the station id as those are what changed when I took the batteries out. The last 8 bits are probably a checksum? But I'm not too familiar with different checksum techniques, I've tried a couple of things but haven't been able to work that out.
At least I know I'm on the right track because I've got the temp/humidity! But my main problem now is determining where the transmission starts. It doesn't seem to send any sort of start sequence (the preceding 1s are noise/indistinguishable from noise).